Sea stars, often recognized by their distinctive radial symmetry, are fascinating invertebrates belonging to the phylum Echinodermata. These marine animals inhabit all the world’s oceans, thriving in diverse environments from warm tropical waters to frigid polar regions and from intertidal zones to abyssal depths. They display a wide range of colors and sizes, with most species typically featuring a central disc and five arms, although some can possess many more. Sea stars play various roles in marine ecosystems, often acting as predators of benthic invertebrates.
Marine Animals That Prey on Sea Stars
Despite their tough exterior, sea stars face predators in the marine environment. Various fish species, including sharks, rays, and other large bony fish, prey on them. These fish often possess specialized mouthparts and strong jaws to consume sea stars. For instance, nurse sharks, horn sharks, and Port Jackson sharks can break through the sea star’s bony outer skeleton to reach the soft tissues inside.
Crustaceans like crabs and lobsters also opportunistically feed on sea stars. Crabs, such as the red king crab, use their powerful claws to tear apart the sea star’s body. Lobsters similarly employ their strong claws to break through the sea star’s armor. Sea otters, while primarily feasting on other invertebrates like sea urchins, have also been documented to consume sea stars.
Other invertebrates, including predatory sea stars, prey on their own kind. For example, the morning sun star ( Solaster dawsoni ) is known to feed predominantly on other sea star species. Some large marine snails may consume sea stars. Seabirds, such as gulls, occasionally prey on sea stars, using their sharp beaks to break through the tough outer layer.
How Sea Stars Protect Themselves
Sea stars have developed several defense mechanisms to deter predators. Their calcified plates, called ossicles, embedded within their skin provide a robust, armor-like exterior, giving them the common name “spiny skin.” Many species further enhance this physical protection with sharp spines that make them difficult for predators to handle or consume. These spines effectively prevent predators from putting the sea star into their mouths.
Beyond physical defenses, some sea star species employ chemical deterrents. Many contain saponins in their body walls, which are unpleasant-tasting to predators. This chemical defense can make them unpalatable. Certain species, like Astropecten polyacanthus, can produce potent toxins such as tetrodotoxin, a powerful nerve-blocker. Some “slime stars” can release large quantities of repellent mucus when agitated.
Sea stars also exhibit autotomy, the ability to intentionally shed an arm when attacked. This allows the sea star to escape danger by sacrificing a limb, which may continue to move and distract the predator. Specialized tissues at the base of the arm facilitate a clean break and minimize fluid loss. Furthermore, some sea stars utilize camouflage, blending into their surroundings with varied colors and patterns to avoid detection. Certain species can also burrow into sand or sediment, leaving only an inconspicuous imprint, to evade predators.
Sea Star Regeneration and Survival
Sea stars can regenerate lost body parts, a crucial factor in their survival against predation. If an arm is lost due to an attack or other injury, the sea star can regrow a replacement. This regeneration process involves specialized cells that form new tissue and can take several months to over a year to complete.
In many species, a sea star can regenerate an entire new arm as long as a significant portion of its central disc remains intact. Some tropical species possess an extraordinary capability, where a single severed arm, particularly if it includes a part of the central disc, can regenerate into an entirely new sea star. This regenerative capacity allows sea stars to recover from potentially fatal injuries, highlighting their resilience in the face of predatory encounters.